The present invention relates to a heat dissipating structure for an electronic control device (ECU).
FIG. 21 shows a conventional circuit board (i.e. printed circuit board) 110 which mounts electronic components 111 and is disposed in a casing of an electronic control device. The heat generated from a heat generating element 112 mounted on the circuit board 110 is transferred via a heat dissipation member 101 to a casing 100 as shown in FIG. 22. The heat dissipation member 101 is preferably used in an ECU of an automotive vehicle as a means for cooling the heat generating element 112 when the heat generating element 112 has high temperatures during its operation. The heat dissipation member 101 is usually an elastic substance represented by rubber or a resin adhesive or grease having improved heat dissipation properties. The heat dissipation member 101 is sandwiched between the casing 100 and the heat generating element 112 as shown in FIG. 22, or is sandwiched between the casing 100 and the circuit board 110 as shown in FIG. 23.
The heat generating element 112 used in this electronic control device is an element generating a great amount of heat in response to large current supplied thereto. Usually, a power MOS transistor or a power diode can be preferably used as the heat generating element 112. Meanwhile, recently developed SMD-type MOS transistors are excellent in compactness and operable under large currents and are accordingly preferably mountable on a circuit board of an electronic control device. In this respect, it is very important to enthusiastically continue engineering development activities for effectively cooling such compact electronic components with a smaller heat dissipating area. These electronic components have the capability of controlling other electronic components with large currents, and accordingly have an important role in the functions of ECU. Furthermore, these electronic components are decisive components which substantially determine the quality of product.
On the other hand, if a gel or other comparable material having fluidity is used as the heat dissipation member 101, although no cracks will occur when a stress is applied on the electronic control device, the heat dissipation member 101 will undesirably shift from a predetermined position when the heat dissipation member 101 or the casing 100 receives an external force such as shock or vibration. In other words, the heat dissipation member 101 will not be able to effectively show its heat dissipation properties.
In this respect, it is possible to increase the surface roughness of the casing as a method for preventing undesirably shifting of the heat dissipation member 101. However, completely suppressing the shifting of heat dissipation member 101 is difficult as long as the heat dissipation member 101 is made of a material having fluidity. Furthermore, as disclosed in the Japanese Patent Application Laid-open No. 2003-289191, as one of preferable embodiments, it is possible to provide a projection (i.e. dam) on a surface on which the heat dissipation member 101 is disposed. According to this method, the heat dissipation member 101 does not shift undesirably. However, this method requires specifying the layout of heat generating element 112 beforehand. When the circuit boards 110 to be handled have various layouts of heat generating element 112, it is necessary to prepare small quantity but many kinds of casings 100 for these circuit boards 110. The cost of casing 100 will increase.